How is limestone used to make cement?

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Limestone is one of the two key components required to make cement; the other is clay. To make cement powder, limestone and clay are ground into a powder, mixed together in the proper proportions and then fed into a rotary kiln, which heats the raw materials to around 2,700 degrees Fahrenheit.

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Although limestone and clay are the main components of cement, very small amounts of aluminum, iron or gypsum are also typically required. Limestone is used due to its high content of calcium oxide, which is the main component of cement and usually makes up around 65 percent of the final product. The amount of clay used depends on its content of silicon oxide, which makes up approximately 20 percent of cement powder.

The cement powder that is produced by heating the materials binds together with water to eventually harden. This powdered cement is typically mixed with other materials to create concrete, mortar and other building materials.

Concrete is formed by mixing sand, rocks and gravel, which bind within the cement to produce a much harder product that sets up like stone. Mortar is made by mixing cement powder with water, sand and lime. It is mostly used to form bonds between bricks or tiles.